is it my stuffit?
 

I downloaded Mp3 rage, and when i double clicked, stuffit opened but didn't expand the file. Then I downloaded Mactella, and the same thing happened. Are the files corrupt or is my expander to blame?

Try dragging and dropping the file over stuffit expander, that should work. Double clicking might not if the icon of the files is generic, because then the mac has no idea of what to open it with